MGCB Wildcard Support

Added wildcard support for content items in the MGCB command line tool.

This implementation follows the wildcard rules defined in the "Remarks" section of Directory.EnumerateFiles(). http://msdn.microsoft.com/en-us/library/dd413233(v=vs.110).aspx

I'll update the Wiki once the PR has been merged.

We also noticed a problem in Texture.GetPitch(). The fix was accidentally committed and added to this pull request, though it's still valid.